The aim of this study was to find out the normal range of penile duplex Doppler parameters with pharmacostimulation of 40 micrograms prostaglandin E1 and to assess the repeatability and clinical value of the method. Maximal systolic velocity increase (SVImax) is presented as a new flow parameter. 10 potent and 82 impotent patients were investigated. Peak systolic velocity values were significantly higher when recorded at proximal than at distal penis. Repeatability of SVImax was fairly good (coefficient of variation = 0.18). SVImax ranged from 32 to 100 cm/s in 10 control subjects. The distribution of SVImax values in patients grouped according to the number of arteriosclerotic risk factors indicates that this parameter may be useful in the diagnosis of arteriogenic impotence.